Nifty Assignments 2005Photomosaics

Rich PattisComputer Science DepartmentCarnegie Mellon UniversityPittsburgh, PA 15213email: pattis@cs.cmu.edu

Overview

What are Photomosaics ® + Examples Programming Concepts Programming Options Contests and Databases Patent Implications

® Photomosaic is a registered trademark of Runaway Technology

What are Photomosaics

A mosaic is a image rendered by a large number of small objects (historically glass and stone)

In a photomosaic, the image is a large picture, which is rendered from smaller pictures Viewed up close, the smaller pictures should be

identifiable; from afar they integrate into the image Often there is a relationship between the two:

An artist rendered from his/her art works A student rendered from his/her classmates A campus landmark rendered from campus photos …your students will come up with “interesting”

combinations, guaranteed to upset someone: its art!

Database Pictures

Each database picture is rectangular, with the same aspect ratio(here photos are square)

Excerpt from a database of CD covers, containing about 1,200 pictures.

A Large Image to Render

Seymour Cray

The Image Rendered by 980 CD Covers

Limiting 10 reuses of any database picture with a minimum distance of 3 between reused pictures

(it helps to squint)

Don Knuth Rendered by 900 Student Photos

Full Size Student Photo

The Assignment

Write a program that produces photomosaics The minimal program must…

Read a database of pictures, displaying it Displaying a database ~ constructing a photomosaic, spatially

Read an image to render Render/display image (regions->database pictures)

Optional (simple vs. complicated assignment) Square vs. Rectangular picture database Sampling size (increase/decrease rendered image size) Built-in vs. plug-in similarity metric(s) Special constraints on rendering: reuse/distance Input/Calculate/Output vs. GUI (via MVC pattern)

Programming Concepts

Arrays 1-d array of Picture objects (in a picture database) 2-d array of pixels (“implicit” in each picture)

Loops Reading all the Picture files in a folder Examining all the pixels in pictures to summarize them Scanning regions in the Image to render Scanning for the “closest” match in the database

Using many classes to build an application Reading Javadoc

The FileSelector and Picture classes Metric interface

Major Provided Components

FileSelector class Easy interface to file-selection GUI

Picture class (about a dozen methods total) constructor makeEmptyPicture Overlay (a region by another picture) display get/set Color (at coordinate), other accessors …

Metric interface copy makeSummary (overloaded for whole picture/region) distanceTo (another Metric object)

More On (plug-in) Metrics

I provide one: Intensity Assume a gray scale Computes/Stores 1 average in [0,255]

Students write at least one: RGB Computes 3 averages (for R, G, B separately) in [0,255]

I provide a Quad Metric-Decorator Implements Metric, constructor has Metric parameter Is a Metric that duplicates its Metric parameter for each

of 4 quadrants (storing more fine-grained data)

Summary delegate; distance delegate (sum of distances) new Quad(new Quad(some metric)) provides 16 regions!

someMetricsomeMetric

someMetric

someMetric

Programming Options

Constraints Maximum reuse for database pictures Minimum distance from a picture to any other use of it Spiral rendering from center (vs. top-down/left-right)

Color shifting to increase database size/usefulness Filtering of pictures (e.g., color -> gray scale) Control Flow

Input/Calculate/Output Menu (but still text) Driven (write as “Model”) Full-blown GUI

I have students write the Model as an earlier assignment (providing them with a textual View/Controller), then have them write a full MVC GUI at the end of the semester

Contests: Something for Everyone

Best Metric (on instructor database and image) Best Art: (on student database image)

Use the Pritchard Scale If the photomosaic's score for perfection is plotted along

the horizontal of a graph, and its importance is plotted on the vertical, then calculating the total area of the curve yields the measure of its greatness.

Quick Rendering: Severe Time Limitations Best Databases found or created

Database Sources

Google the Web I’ve found cd covers, beer labels, Christmas

cards, etc. (tools are available to batch convert pictures to the appropriate sizes)

Ask students They do even better googling If they have digital cameras, create your own

Tools: Converting Movies -> Frames Cheating: shift pictures

redder/greener/bluer Students can easily write filters for the Picture class

Patent Issues

This topic is a 50 minute talk itself! I am not a lawyer; here are some “facts”

Creating photomosaics is patented Unlike copyright, there is no fair use Can teach how to make them, but not make them

Owner wouldn’t license patent for class use Damages are based on lost income David Evans (UVa) has made photomosaics;

published in campus newspaper and on web Photomosaic program on the web

Will your school support you in a lawsuit? Talk to your school’s legal folks

Using Blobs

Students can use bw/color blobs to test their programs without ever producing a “photomosaic”

Database of 1000 random colors